Binary and ternary iron-nitrogen, iron-nitrogen-carbon systems
Thermochemical treatment theories - Nitriding - Nitrocarburizing- Iron-nitrogen binary systems and iron-nitrogen ternary systems - Compound layer

The iron-nitrogen equilibrium diagram (figure 1) highlights the presence of the different phases ε, γ′ and α, i.e. three single-phase domains:

• a solid solution of nitrogen insertion in iron α of centered cubic structure called "diffusion layer". This is the seat of the diffusion/precipitation mechanism in the presence of chromium, vanadium, aluminum, titanium etc., in solution. This mechanism is at the origin of hardening by nitride precipitation and compressive stressing of the steel surface;

• a non-stoichiometric γ′ - Fe₄N_1-x intermetallic phase between 400 and 680°C (see figure